Chronic diseases are the leading cause of death in the world, accounting for over 60 % of all fatalities. Decreased levels of the tripeptide glutathione (GSH) are well-known to be associated with chronic diseases and are of interest in monitoring disease progression and therapeutic interventions. For example, recent studies show that monitoring whole blood glutathione (GSH) levels can be of benefit towards diagnosing asymptomatic heart failure and mitochondrial disorders. GSH monitoring is also useful in the health assessment of patients with chronic renal disease or post-operative open heart surgery. However, reported levels of GSH in both healthy subjects and patients exhibit inter-laboratory variation. Plasma GSH levels are often reported despite the fact that they account for less than 0.5 % of the circulating GSH. Divergent sample processing and conjugation steps propagate inter-laboratory variability, as they result in varying degrees of sample oxidation and labeling. In order to achieve consistent and efficient GSH monitoring, the major goal of this proposal is to develop a fluorescent indicator that functions directly in minimally-diluted whole blood. In order to achieve this goal, the following specific aims are proposed: 1. Design, synthesis and evaluation of NIR-active GSH-selective indicators. Based on the preliminary data referred to above, our working hypothesis is that highly selective indicators for GSH can be designed to bind GSH via multipoint supramolecular interactions and produce concomitant fluorescence signals without optical interference from hemoglobin or other blood components. 2. Develop methodology for detection and quantitation of GSH in whole blood. We postulate, again on the basis of our preliminary data, that selectivity and sensitivity for GSH over a disease-relevant range can be achieved in human blood via the design of GSH-selective NIR active probe-containing receptors. The studies proposed in this aim are thus focused on optimization and demonstration of the utility of the proposed design principles and synthetic indicators via extensive evaluation and validation studies.